1. Field of the Invention
The present invention generally relates to anatomical prostheses and more specifically an artificial ankle joint for use as an ankle between the foot prothesis and leg prosthesis in an artificial limb. The artificial ankle joint includes a foot plate attached to a foot prosthesis, a leg plate attached to a leg prosthesis, a stem assembly and bearing assembly connected between the plates in which the bearing is a spherical bearing oriented vertically and including an inner race connected to the leg plate about an axis generally horizontal when the ankle joint is in use and an outer race connected with the stem assembly and foot plate. Resilient structure extends between the plates for providing a degree of resistance to relative movement of the plates and includes a heel spring enclosing the stem assembly and a toe spring spaced from the heel spring with both the toe and heel springs extending between the plates. The stem includes a unitary or two piece unit anchored to the foot plate at one end and including a vertically disposed spherical bearing assembly connected to the leg plate at its other end to enable relative pivotal movement of the foot prosthesis in any angular direction with respect to the leg prosthesis and enabling limited swivelling movement of the foot prosthesis in relation to the leg prosthesis. This enables the articulated ankle to closely simulate all movement capabilities of a natural ankle.
2. Description of the Prior Art
My prior U.S. Pat. No. 4,764,172 for Articulated Ankle issued Aug. 16, 1988 discloses an ankle joint for use in an artificial limb which utilizes a foot plate, leg plate, stem and a heel spring and toe spring with the stem including a horizontally disposed bearing and a structure enabling adjustment of the stem and attachment of the stem to the foot and leg plates. This patent and the prior art cited of record in that patent are made of record herein. The prior art does not disclose the specific structure of the articulated ankle joint of this invention including the specific arrangement of the stem and vertically disposed bearing interconnecting the stem and leg plate and cushioning spacers between the heel spring and plates. Attached hereto from the publication "Orthotics and Prosthetics" dated Spring 1987 is an article entitled "Dual-Ankle Spring (D.A.S.) Foot-Ankle System" by Jerome P. Voisin, which discloses the use of anterior and posterior springs between plates with an Achilles band controlling relative movement to some degree. This article discusses various problems and developments in this field of endeavor and certain of the developments relating to this subject matter including certain prior patents. This article also fails to disclose the specific structure of this invention.